Anxiety disorders are a cluster of debilitating conditions that affect more than 18% of the adult US population (Kessler et al., 2005). When anxiety is high, whether catalyzed innately (e.g.Generalized Anxiety Disorder (GAD)), or by a traumatic event (e.g. Post-Traumatic Stress Disorder (PTSD)), a patient is severely stressed and in anguish, often becoming isolated and unable to participate in daily life. Anxiety disorders also pose a substantial economic burden on our society, estimated to cost almost $34 billion in US spending in 2013 alone (Shirneshan et al, 2013). A thorough understanding of the neural circuits underlying generalized fear and the ability to differentiate threat from safety is critica to effectively treating anxiety. The goal of the proposed research is to identify how interactions within the prefrontal-basal forebrain-amygdala circuit contribute to processing threat and safety. The basal forebrain has dense inhibitory and cholinergic projections to the amygdala, and both of these neurotransmitters are known to play an important role in shaping amygdala activity during emotional learning. However, we do not yet have a good understanding how different neurochemical inputs from the basal forebrain impact amygdala physiology and affect behavior. To address this, aim 1 of the proposal is to establish the role of inhibitory signaling from the basal forebrain to the amygdala during threat and safety processing. In contrast to the basal forebrain-amygdala, connectivity between the prefrontal cortex and the amygdala has received more attention for its role mediating fear discrimination. However, the prefrontal cortex is known to drive inhibitory cells in the basal forebrain (Guyengsi et al, 2008) and inhibitory cells from the basal forebrain have known projections to the amygdala (McDonald et al., 2011). Thus, the basal forebrain may serve as an important interface between the prefrontal cortex and the amygdala during anxiety processing. To test this idea, Aim 2 of the proposal is to isolate the contribution of the indirect prefrontal-basal forebrain-amygdala projection to differentiating threatening and safe stimuli. These studies will employ a combination of clinically relevant behavioral paradigms, large-scale neurophysiological recordings, novel anatomical tracing methods and optogenetic control of circuit function during behavior. The prefrontal-basal forebrain-amygdala network has the potential to be critical for regulating threat-related amygdala activity and affective processing. The proposed research is necessary for a better understanding of how this understudied circuit contributes to adaptive aversive learning. This work will be essential for building a translational model for generalized fear, which can lead to targeted therapies for patients suffering from disorders of learned anxiety, such as PTSD.